The present invention is directed to a roll or drum capable of rapidly transferring large quantities of heat to a material in contact with the drum surface. The roll is especially well adapted for use in a press of the type in which a drum is wrapped with a tensioned belt holding an interposed material tightly in contact with the drum.
One belt and drum press of the general type described above is disclosed in U.S. Pat. No. 3,319,352 to Haigh. A preferred press is shown in U.S. Pat. No. 4,710,271 to Miller. This latter inventor shows a system which includes two belt tensioning rolls which also form nip contact with the drum through the interposed belt. Preferably, additional idler nip rolls are also included. One particular advantage of this press is the balanced construction whereby pressing forces are not transmitted to the supporting framework. This enables the drum to be floating with respect to the nip rolls. In one version of the press the drum is a hollow cylinder which can be directly heated. A number of optional construction patterns are shown which enable relatively high heat flux without undue stress caused by a high temperature differential across the drum. In addition to the direct heated versions, an alternative version employs a steam heated drum. Here the drum is made with a thin outer shell to obtain maximum heat transfer. This is supported by a series of longitudinal ribs fixed to a relatively heavy walled inner drum which withstands the load stresses applied by the belt and nip rollers.
The drums in the direct fired versions of the above press suffer from competing requirements. The shell must be of adequate thickness to withstand the very high loads imposed at the nip zones. On the other hand it must be relatively thin to avoid the high thermal stress which would be created by a high temperature differential across the drum wall. These requirements tend to force a compromise solution which results in a lower than desired heat transfer rate. The other versions of the press using steam heated drums similarly suffer from the fact that steam heat begins to be impractical over 400.degree. F. because an increasingly adverse pressure/temperature relationship requires excessive pressure levels.
In an effort to resolve the competing problems of obtaining high temperature levels at extremely high rates of heat flow from the drum to the contacting work material, while maintaining adequate drum strength and integrity, the present inventor has sought solutions quite different from those described in the above noted U.S. Pat. No. 4,710,271. The problem is exacerbated by the diversity of loading on the preferred press; i.e., very high concentrated nip loads and extensive large area distributed loads from the tensioned belt. Paper machine widths may be as great as 400 inches and nip pressures in press and calendar sections are very high. Roll deflection can become a very serious additional problem unless extremely heavy construction is used.
Hydraulically supported rolls are well known in the paper and printing industry as an answer to the deflection problem. These are typically designed with a relatively heavy rotating shell supported on a fixed inner core portion. A number of hydraulic bearing support elements are arranged longitudinally along the core. These can be adjusted to resist deflection caused by an opposing roll and to obtain uniform nip pressures. Using general systems of this type, the overall size and weight of the resulting rolls can be reduced significantly over that which would be required for solid rolls and deflection avoided entirely. There are other advantages as well in that deflection can be controlled differentially from side to side across the rolls if desired.
Reference is made here to a number of earlier patents which are generally related to the present invention. All of these deal with hydraulically supported rolls in which a rotating shell is supported on a stationary core. Typical of the rolls of this type is the one shown by Marchioro in U.S. Pat. No. 4,183,128. Here a heavy rotatable shell is supported on a plurality of longitudinal jack-like hydraulic pressure elements, each of which has individual pressure regulators located in the fixed support.
Spillman et al., in U.S. Pat. No. 3,802,044, show a heavy shell roll held on a multiplicity of individual fixed bearings located on the core portion. The bearings can individually adjust to shaft deflection without loss of proper face-to-face contact at the interface with the shell. FIG. 9 of this patent shows the roll having angularly spaced apart hydraulic supports symmetrically arranged to resist the forces imposed by four outside rolls making nip contact.
Mohr, in U.S. Pat. No. 3,853,698, shows an extended nip press having a fixed hydraulically loaded anvil section and a superposed hydraulically supported press roll.
In U.S. Pat. No. 3,362,055, Bryce shows a heavy shell supported on a fixed core divided angularly into multiple compartments filled with a hydraulic oil. The roll can be further divided into two overall sections having differentially regulated oil pressures.
A pressure roll known as a "swimming" roll is widely available in the paper industry. In a roll of this type the heavy outside shell is supported on a core having opposed longitudinal seals approximately 180.degree. apart. The roll is oriented so that it forms a nip with an opposing roll. The compartment facing the nip zone is filled with pressurized hydraulic oil while the other compartment is generally left empty.
One inventor recognized the situation in which different load types affect the deflection of a roll in a paper mill environment. Skaugen, in U.S. Pat. No. 3,430,319, described a breast or couch roll for a paper machine which is differentially hydraulically supported. One side of the roll is supported on a longitudinal fluid bearing designed to compensate for defection of the roll under its own weight. Angularly displaced from this is a second longitudinal fluid bearing which counters the resultant of the forces imposed by a traveling paper machine wire partially wrapped around the roll.
All of the above rolls are built with relatively thick shells. In general these shells will be a minimum of about 20 mm in thickness and may range up to 105 mm or even greater. Very commonly these rolls will be made from chilled cast iron. The present inventor is aware of two other hydraulically supported rolls having thin shell walls. One of these is detailed in West German Application No. 31 02 526 to Hauser et al. This invention is directed to an extended nip press roll. The outer shell is made of a flexible plastic material such as polyurethane. In U.S. Pat. No. 4,358,993, Spillman et al. show an internally heated, hydraulically supported roll suggested for the preparation of food products. This device has a thin flexible metal shell having multiple angularly displaced hydraulic support points. The hydraulic fluid which serves at the support points as a fluid bearing medium is heated and this also serves to heat the shell. Baffle strips divide the interior portion of the roll into different temperature zones. The volumes between these baffles form oil collection sumps where oil which leaks from the bearings is picked up for return to the heater. In this particular device the shell path and configuration is not fully circular but is somewhat tear drop-shaped in configuration. A drive roll is located inside the shell at the point of the tear drop. Because of this asymmetrical construction, which causes continual flexing, the shell would be limited to a very thin material, typically less than 2 mm in thickness.
None of the above rolls would be capable of solving the problem described earlier; i.e., that of operating at a high temperature to achieve a high rate of heat flow from the drum to a contact web while still maintaining adequate drum integrity under heavy nip and distributed loads. One solution to the problem appears to be found by hydraulically supporting a thin rotating drum shell which is mounted on a stationary load bearing core. The resulting drum, consisting of the core and shell, is filled with a hot heat transfer fluid which can also serve as the hydraulic support medium for the shell. In this way internal temperatures as high as 700.degree.-800.degree. F. are possible. The use of a very thin shell permits a high rate of heat transfer without inducing an unacceptable thermal stress in the shell material. Close matching of the internal hydraulic support to the external loads is necessary to minimize shell stress from mechanical loading.